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Asynchronous Transfer Mode (ATM)

Computer Networks. Asynchronous Transfer Mode (ATM). ATM Outline. ATM Introduction Motivation for ATM Architecture Design Assumptions ATM Adaptation Layers Old ATM Design Revised ATM Design AAL Details MPLS. ATM Introduction. DCC 9 th Ed. Stallings.

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Asynchronous Transfer Mode (ATM)

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  1. Computer Networks Asynchronous Transfer Mode(ATM)

  2. ATM Outline • ATM Introduction • Motivation for ATM Architecture • Design Assumptions • ATM Adaptation Layers • Old ATM Design • Revised ATM Design • AAL Details • MPLS Computer Networks ATM

  3. ATM Introduction DCC 9th Ed. Stallings ITU-T lead the standards development. ATM Forum ensures interoperability among private and public ATM implementations. ATM commonly used to implement WANs. DSL uses ATM for multiplexing and switching. ATM still used as a backbone in some IP networks. Computer Networks ATM

  4. Issues Driving LAN Changes • Traffic integration • Voice, video and data traffic • Multimediabecame the ‘buzz word’ in the 1990s • One-way batch Web traffic • Two-way batch voice messages • One-way interactive Mbone broadcasts • Two-way interactive video conferencing • Quality of Service guarantees (e.g. limited jitter, non-blocking streams) • LAN interoperability • Mobile and wireless nodes Computer Networks ATM

  5. Stallings’ “High-Speed Networks” Backbone Computer Networks ATM

  6. Stallings’ “High Speed Networks” Computer Networks ATM

  7. cells cells cells … ATM Adaptation Layers Voice AAL A/D s1 , s2 … Digital voice samples Video AAL Compression A/D compressed frames picture frames Data AAL Bursty variable-length packets Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  8. Asynchronous Transfer Mode (ATM) Voice Data packets MUX Wasted bandwidth Images TDM 4 3 2 1 4 3 2 1 4 3 2 1 ATM 4 3 1 3 2 2 1 Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  9. ATM • ATM standard (defined by CCITT) was widely accepted by common carriers as mode of operation for communication (particularly BISDN). • ATM is a form of cell switching using small fixed-sized packets. Basic ATM Cell Format 48 Bytes 5 Bytes Header Payload Computer Networks ATM

  10. ATM Conceptual ModelFour Design Assumptions 1. ATM network will be organized as a hierarchy. • User’s equipment connects to networks via a UNI(User-Network Interface). • Connections between provided networks are made through NNI (Network-Network Interface). 2. ATM will be connection-oriented. • A connection (an ATM channel)must be established before any cells are sent. Computer Networks ATM

  11. ATM Interfaces DCC 9th Ed. Stallings Computer Networks ATM

  12. ATM Connections • two levels of ATM connections: virtual path connections (VPC) virtual channel connections (VCC) • indicated by two fields in the cell header: virtual path identifier VPI virtual channel identifierVCI Computer Networks ATM

  13. ATM Virtual Connections • Virtual Path Connection (VPC) • bundle of Virtual Channel Connections (VCC) with same end points. DCC 9th Ed. Stallings Computer Networks ATM

  14. ATM Conceptual Model Assumptions (cont.) 3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates. 4. ATM must support low cost attachments. • This decision lead to a significant decision: to prohibit cell reordering in ATM networks.  ATM switch design is more difficult. Computer Networks ATM

  15. ATM Cell Formats DCC 9th Ed. Stallings Computer Networks ATM

  16. Payload Type (PT) Field Coding DCC 9th Ed. Stallings Computer Networks ATM

  17. ATM Cell Switching 1 1 voice 67 Switch … video 2 67 N 25 75 video 32 voice 5 25 1 32 67 data 3 39 32 3 39 32 video 61 data 6 … 61 2 67 … N video 75 N Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  18. Two Levels of ATM Switches a VP3 VP5 a b ATM Sw 1 ATM Sw 2 b ATM DCC c ATM Sw 3 c d e VP2 VP1 d ATM Sw 4 e Sw = switch Digital Cross Connect Only switches virtual paths Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  19. ATMProtocol Architecture • ATM Adaptation Layers (AAL) – the protocol for packaging data into cells is collectively referred to as AAL. • Must efficiently package higher level data such as voice samples, video frames and datagram packets into a series of cells. Design Issue: How many adaptation layers should there be? Computer Networks ATM

  20. ATMProtocol Architecture Management plane Plane management Control plane User plane Layer management Higher layers Higher layers ATM Adaptation Layer ATM layer Physical layer Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  21. ATMin the Protocol Stack User information User information AAL AAL ATM ATM ATM ATM PHY PHY PHY PHY … End system End system Network Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  22. Original ATM Architecture • CCITT envisioned four classes of applications (A-D) requiring four distinct adaptation layers (1-4) which would be optimized for an individual application class: • Constant bit-rate applications CBR • Variable bit-rate applications VBR • Connection-oriented data applications • Connectionless data application Computer Networks ATM

  23. ATM Architecture An AAL was further divided into: • Convergence Sublayer (CS) • manages the flow of data to and from SARsublayer. • Segmentation and Reassembly Sublayer • (SAR) • breaks data into cells at the sender and reassembles • cells into larger data units at the receiver. Computer Networks ATM

  24. OriginalATM Architecture Computer Networks ATM

  25. Physical Layer ATM Adjustments ATM layer Transmission convergence sublayer Physical layer Physical medium dependent sublayer Physical medium Computer Networks ATM

  26. Original ATM Architecture • The AAL interface was initially defined as classes A-Dwith SAP (Service Access Points) for AAL1-4. • AAL3and AAL4were so similar that they were merged into AAL3/4. • The data communications community concluded that AAL3/4was not suitable for data communications applications. They pushed for standardization of AAL5(also referred to as SEAL – the Simple and Efficient Adaptation Layer). • AAL2was not initially deployed. Computer Networks ATM

  27. RevisedATM Architecture Computer Networks ATM

  28. Revised ATM Service Categories Computer Networks ATM

  29. QoS, PVC, and SVC • Quality of Service (QoS) requirements are handled at connection time and viewed as part of signaling (e.g., RSVP). • ATM provides permanent virtual connections and switched virtual connections. • Permanent Virtual Connections (PVC) permanent connections set up manually by network manager. • Switched Virtual Connections (SVC) set up and released on demand by the end user via signaling procedures. Computer Networks ATM

  30. AAL 1 (b) CS PDU with pointer in structured data transfer 47 Bytes AAL 1 Pointer 46 Bytes 1 Byte optional (a) SAR PDU header SNP Seq. Count CSI 1 bit 3 bits 4 bits Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  31. 47 47 47 1 47 1 47 1 47 H H H 5 48 5 48 5 48 AAL 1 User data stream Higher layer … b1 b2 b3 CS PDUs Convergence sublayer SAR PDUs SAR sublayer H H H ATM Cells ATM layer Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  32. AAL 3/4 CS and SAR PDUs (a) CPCS-PDU format Trailer Header AL Etag Length CPI BtagBASize Pad CPCS - PDU Payload 1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes) (b) SAR PDU format Header (2 bytes) Trailer (2 bytes) LI CRC ST SN MID SAR - PDU Payload 2 4 10 44 6 10 (bits) (bytes) (bits) Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  33. 2 44 2 2 44 2 2 44 2 AAL 3/4 Higher layer Information User message Service specific convergence sublayer Assume null Pad message to multiple of 4 bytes. Add header and trailer. Common part convergence sublayer H Information T PAD 4 4 Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload. … SAR sublayer ATM layer … Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  34. AAL 5 Convergent Sublayer Format UU CPI Length CRC Pad Information 0 - 65,535 0-47 1 1 2 4 (bytes) (bytes) SAR Format ATM Header 48 bytes of Data 1-bit end-of-datagram field (PTI) Leon-Garcia & Widjaja: Communication Networks Computer Networks ATM

  35. AAL 5 Information Higher layer Service specific convergence sublayer Assume null Common part convergence sublayer Information T PAD … SAR sublayer 48 (0) 48 (0) 48 (1) ATM layer … Leon-Garcia & Widjaja: Communication Networks PTI = 1 PTI = 0 PTI = 0 Computer Networks ATM

  36. STM-1 (STS-3) Payload for SDH-Based ATM Cell Transmission Computer Networks ATM

  37. MPLS (Multi Protocol Label Switching) Computer Networks ATM

  38. The Nortel Networks Passport 8600 Routing Switch designed for high-performance Enterprise, carrier, and service provider networks. As a chassis based Ethernet switching platform, the Passport 8600 series provides wire speed L2-L7 traffic classification, filtering, forwarding and routing. Hardware based wire speed performance enables fast and efficient traffic classification, policy enforcement and filtering. Provides wire speed L2- L7 traffic classification. Computer Networks ATM

  39. The Nortel Networks Passport 8600 Routing Switch Multi-layer redundancy with five 9’s reliability Integrated intelligent bandwidth connectivity for 10/100/1000 Ethernet, ATM, PoS,10 Gig and WDM Seamless LAN/MAN/WAN connectivity Eight policy enabled hardware queues per port 512 Gigabits per second backplane switch capacity. Computer Networks ATM

  40. Nortel Ethernet Routing Switch 8600 • Avaya Switch ERS 8600 • Configurable as a 1.440 Terabit Switch cluster using SMLT • 10 Gigabit Ethernet • Packet Over SONET • 6 OC-3 or 3 OC-12 ports • ATM • 4 firewall or IDS Computer Networks ATM

  41. ATM Summary • Motivation for ATM Architecture • Four Design Assumptions • ATM Hierarchy • UNI,NNI, VPI, VCI, two switch levels • Old ATM Design • Convergence Sublayer (CS), Segmentation and Reassembly Sublayer (SAR) • ATM Adaptation Layers • AAL1-4 Computer Networks ATM

  42. ATM Summary • New ATM Design • PVC, SVC • AAL Details • AAL1, AAL3-4, AAL5 • Multi-Protocol Layer Switching (MPLS) • Passport Switch Computer Networks ATM

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